How to Choose an Air Purifier: 7 Checks Before You Buy

This guide shows you how to choose an air purifier by checking seven things before you pay: room size and CADR, filter type, noise, power use, filter cost, sensors and the warranty you get in Nepal. Each check comes with the number to look for, so you can compare any two models side by side.

An air purifier pulls room air through a fan, traps particles such as dust, pollen and smoke in a filter, and blows clean air back out. It keeps doing this all day, so the air in the room gets cleaner every hour it runs. Blueair adds an electric charge to particles before the filter so it can catch very small ones without a dense, noisy filter. You can read how that works on our Blueair technology page.

Short on time? Answer a few questions below and the finder sizes a purifier for your room and shows the working.

The 7 checks before you buy an air purifier

1. Room size in sq ft and CADR

Start with the room, because a purifier that is too small for it will never catch up. Measure the length and width in feet and multiply them. A room of 10 ft by 14 ft is 140 sq ft.

Then look at CADR, the Clean Air Delivery Rate. It tells you how much clean air the purifier puts out, tested to AHAM standards. Each model has three CADR figures, for dust, pollen and smoke. Smoke particles are the hardest to catch, so the smoke figure is the one to size with.

AHAM’s rule is simple: the smoke CADR in cfm should be at least two-thirds of the room’s area in sq ft. For our 140 sq ft room that is 93 cfm. One cfm is about 1.7 m³/h, so you need roughly 160 m³/h. The Blue Pure 411 has a smoke CADR of 180 m³/h, so it covers this room.

Two more things change the answer. Room ratings assume an 8 ft ceiling, so pick a model rated for a bigger room if your ceiling is higher. And an open kitchen, dining and living area counts as one space, so add the areas together. Our CADR and room size guide covers air changes an hour, and the open-plan guide covers big connected spaces.

2. Filter type: HEPA, HEPASilent and carbon

The filter decides what gets caught. A true HEPA filter, by the US standard, captures 99.97% of particles at 0.3 micron. Be careful with words like “HEPA-type” or “HEPA-like”. They are not the same standard.

Blueair’s HEPASilent filtration captures at least 99.97% of airborne particles down to 0.1 micron, which is smaller than the HEPA test size. That covers PM2.5, the fine dust behind most bad AQI days. Our HEPA filter guide explains the standard, and the HEPA air purifier page lists the models.

Activated carbon is a separate layer for smells and some gases from cooking, incense and traffic. If odour matters to you, check that the filter name says “carbon”. Skip purifiers that make ozone on purpose. Read more in do air purifiers produce ozone, and see air purifier types explained for UV and ionizers.

3. Noise in dB at the speed you will use

Every purifier is quiet on low and loud on high, so look at the speed you will actually use. For a bedroom that is the lowest speed, because that is where it runs at night.

In our range the lowest speed starts at 17 dB on the Blue Pure 411 and 23 dB on the Blue 3610. On top speed most models sit between 45 and 56 dB, and the large Classic 680i reaches 62 dB. Run high speed when you are out or for a quick clean, then drop to low. Bedroom picks with their night-time noise are on the bedroom air purifier page.

4. Power in watts and the monthly bill

A purifier runs for many hours, so watts matter. Our models use from 1.5 W on the lowest speed of the Blue Pure 411 up to 100 W on the top speed of the Classic 680i.

Here is the sum for the Blue Pure 411 on top speed, 8 hours a day. 10 W x 8 hours x 30 days = 2.4 units. At NEA’s Rs 9.50 a unit, that is about Rs 23 a month. The filter is the bigger cost: Rs 4,000 every 6 months is about Rs 667 a month. Together, about Rs 690 a month.

The same sum gives about Rs 1,247 a month for the Blue 3410 and Rs 2,170 for the Blue 3610. The full working, with every model, is in our air purifier electricity cost guide.

5. Filter life, filter price and local stock

A purifier is only as good as its next filter. Before you buy, check three things: how long the filter lasts, what it costs, and whether genuine filters are in stock in Nepal.

Blue and Classic filters last about 6 months in normal use. DustMagnet and HealthProtect filters last 6 to 12 months, and the purifier counts the days for you based on how it is used. Dusty months fill a filter faster. In our store, genuine Blueair filters cost from Rs 4,000 (Blue Pure 411) to Rs 22,500 (Classic 680i and HealthProtect 7700 series). Divide the price by its life in months and add it to the monthly cost above.

See every filter and the model it fits in our air purifier filters list, and learn the signs a filter is full in how often to change Blueair filters.

6. Sensors, auto mode and the app

A sensor reads the dust in the air and shows it as a colour or a number. Auto mode uses that reading to speed the fan up when the air gets worse and slow it down when it is clean. You get clean air without touching a button, and you save power on clean days.

Wi-Fi models, such as the Classic 480i, DustMagnet 5440i and HealthProtect 7470i, also connect to the Blueair app. You can check the air from your phone, set schedules and see how much filter life is left. Simple models, such as the Blue Pure 411 and Classic 405, have no sensor and run at the speed you choose. They cost less and work just as well when you set the speed yourself.

7. Warranty and service in Nepal

The warranty is only useful if someone in Nepal will honour it. Buy from a dealer who handles the warranty here, keeps filters in stock and answers when you call.

Genuine Blueair from Clean Air Store comes with a local warranty: 1 year on the Blue series, 2 years on DustMagnet and 3 years on HealthProtect and Classic. Full terms are on our warranty page.

What is different about buying an air purifier in Nepal

Most of the checks above apply anywhere. A few matter more here.

• Genuine stock. Grey imports and copies often carry no warranty you can claim in Nepal, and their filters are hard to find later. Ask for an authorised dealer and a warranty card.
• Filters you can get next year. A cheap machine with no local filter supply stops cleaning once its first filter is full.
• The dry season. From November to May, road and construction dust are at their worst. Plan for filters to fill faster in those months.
• Delivery outside the Valley. We deliver in 1 to 2 working days inside the Kathmandu Valley and 3 to 5 working days to most other cities.

All 7 checks at a glance

Common mistakes when choosing an air purifier

• Buying before you measure. A model rated for 160 sq ft will struggle in a 300 sq ft living room.
• Comparing only the machine price. Over two years the filters can cost more than the difference between two models.
• Expecting one unit to clean the whole house. A purifier cleans the room it is in. See can one air purifier clean the entire house.
• Hiding it in a corner. Walls and furniture block the airflow. Our placement guide shows where it works best.

More slips to avoid, with fixes, are in air purifier mistakes.

Now pick an air purifier for your space

You know what to check. Each page below applies these checks to one kind of room and shows the models that pass.

• Air purifier for home: living rooms, cooking smoke and winter heaters
• Air purifier for bedroom: quiet models for sleep
• Air purifier for baby and kids room: low noise and safe placement
• Air purifier for dust: road and construction dust
• Large room air purifier: open plan and big halls
• Air purifier for office: workdays, meeting rooms and bulk orders
• Affordable air purifier: lowest total cost a month
• Car air purifier: Blueair Cabin for daily drives

Or compare every model and price on one page in our air purifiers in Nepal list, or see how the brands sold here compare in air purifier brands in Nepal.